Declining lake sediment phosphorus release and oxygen deficit following wastewater diversion

Abstract

Lake Sammamish failed to show a predictable response after phosphorus loading was reduced by one-third through waste water diversion in 1968, according to studies during the early 1970s.13 Based on the flushing rate alone, the lake phosphorus concentration should have recovered 90% of its equilibrium level within 4 years. However, phosphorus and chlorophyll-a content or depth of visibility (Sechhi disk) did not change significantly during 1970-75,3 compared to results from a prediversion study in 1964-66.4 Average summer values for surface chlorophyll-a and Secchi depth and annual whole-lake values for phosphorus for the preand post-diversion periods were 5 Mg/L, 3.3 m, and 33 Mg/L, respectively, for the prediversion period and 6.6 Mg/L, 3.4 m, and 27 Mg/L, respectively, for the postdiversion period.